Pipe plug anode



March 1963 H. s. PREISER ETAL 3,081,252

PIPE PLUG ANODE Filed Sept. 30, 1959 Ti or Tu=22 FIG.3

INVENTORS HERMAN S. PREISER FRANK E. COOK United States Patent 3,981,252PIPE PLUG ANODE Herman S. Preiser, West Springfield, and Frank (look,Arlington, Va, assignors to Chemionics Engineering Laboratories, Inc, acorporation of North Carolina Filed Sept. .30, 1959, Ser. No. 843,602

3 Claims. (Cl. 204-196) (Granted under Title 35, U.S. Code (19.52), sec.266) The invention described herein may be manufactured and usedby orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invent-ion relates to a pipe plug anode for the oath Jdicprotection of vessels in which fluid fiows as, for example, metallicpumps in contact with a corroding electrolyte. The purpose of thisinvention is to provide a compact insulated impressed current anodestructure for use in cathodic protection (corrosion protection) ofinternal piping, tanks, pumps and any application where a small anode isneeded for protecting metals in contact with electrolytes-under pressureor vacuum. The anode device is particularly adaptable for service wherewater-tightness of the anode connection is required and wherecompactness is an important consideration.

Heretofore, high capacity, small size, pressure proof anodes have notbeen available for this function. ertain types of heat exchangers havebeen fitted with pipe plugs whichin turn were drilled to receive a zincor iron pencil for means of cathodic protection, but in many cases thebulk of material required to achieve adequate current output withsufficiently long life has been greater than was practical to install ina given space. .Many of these prior devices used a consumable zinc anodewhich galvanically generatedan electric current to cathod-ically protecta tank or heat exchanger by virtue of its relatively higherelectrochemical potential as compared to iron or copper alloys in thestructure under protection; These consumable anodes had a limiteddriving voltage, due to their electrochemical characteristics, whichrequired a large surface area to be exposed to the electrolyte in orderto generate a sufiiciently large cathod-ically protective current.Impressed current systems have also been proposed using consumableanodes which overcome the objection of limited current output but theirshort service life necessitated frequent renewal.

While an object to be cathodically protected, such as a ship in seawatenmay require only 5 milliarnperes per square foot of exposedsurface, a ships pro-pe ler or a high speed pump may require 25 to 50milliarnperes per square foot for adequate cathodic protection since thefriction and turbulence of the Water moving over the blades strips offthe protective layers or" hydrogen atoms. .Also rapidly moving waterwill depolarize the cathode quicker by bringing large amounts ofdissolved oxygen in contact with the hydrogen layer. Thus furtherincreases in anode size were required for rapidly moving propellerblades or impellers.

In order to overcome these difficulties, it is the primary object ofthis invention to provide, as a single article of manufacture, aninsoluble pipe plug anode which may be used in an electrically energizedcathodic protection system that will supply an adequate protectivecurrent without rapid corrosion of the anode.

The invention consists of a dielectric chemically resist ant plasticpipe plug which has a thin central rod for connection to a suitableelectrical power source and an anode disc consisting of platinum coatedtantalum connected to the central rod and mounted on the inner end ofthe pipe plug.

3,081,252 Patented Mar. 12, 1963.

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Another object of this invention is to minimize the tlow resistance ofthe pipe plug anode to the electrolyte by mounting the disc parallel tothe electrolyte flow across the pipe plug and eliminating extensions andprojections from the plug that would otherwise be in the path of flow ofthe electrolyte.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a view in cross-section of a preferred em bodiment of the pipeplug anode;

FIG. 2 is a view, partly in cross-section and partly in schematic form,of an application of the pipe plug anode in a centrifugal pump cathodicprotection system;

and FIG. 3 is. a cross-section view of FIG. '2 taken along lines 3--3.Referring now to thed-rawings, there is shown in FIG. 1 a unitary pipeplug 10 having a body made of a dielectric chemically resistant plasticwith a standard pipe taper threaded section 12 providing an innerend-portion for the plug so as to make a watertight connection with asuitable mating bossing such as on a boat hull or pump casing, a nutsection 14 which is molded or machined so that the pipe plug anode maybe mounted or removed with simple tools, and an upper threaded contactsection 16 providing an outer end-portion for the plug to re.- ceive ascrew connector connected to an electrical power source.

The pipe plug 10, in this case 1 /2 inch IPS, has a central hole 18coaxial with the threaded section 12 to contain a connecting knurledstem 20, preferably made of tantalum, having a diameter of A; of aninch. It is important that the connecting stem 20 and hole 18 berelatively small as compared with the diameter of the threaded section12 so that the plastic plug 10 will deform evenly around itscircumference to fit the mating bossing as the nut section 14 istightened to provide a uniform pressureproof seal. In this case theratio of the diameter of the threaded section 12 to the central hole 18is about 8 to 1.

The anode consists of a 1 inch diameter, .020 inch thick disc 22 oftantalum with a porous, flash surfacecoa-t 24 of .00025 inch thickplatinum. Disc 22 is fitted in recess 25 and is perpendicular to andmuch larger diametrically than the /8 diameter stem. As shown in FIG. 1,the disc 22 is imbedded in an inner end of sect-ion 12 with the innersurface-coat 24 of the disc exposed (the term inner being with respectto the wall in which section 12 is screwed) so that it provides arelatively large cathodic protective surface in contact with theelectrolyte and in line with the direction of flow of the electrolyte. Apotting recess 26 provides room for a potting resin 28 to seal the disc22 in recess 25. This potting resin 28 may be Royalite cement or anepoxy resin.

A second potting recess 30 and resin 32 at the contact section 16 partof the pipe plug 10 seal the other end of the rod 18 and a contact 34made of platinum coated tantalum for connection to a cable connector.

In making the pipe plug anode, the plastic plug 10 may be formed in amold or machined to the shape shown in FIG. 1. The knurled stem 20 isspot welded to the anode disc 22. The stem is buttered With Royalitecement or an epoxy resin and potting recess 26 is filled with the samecement or resin. The stem and anode subassembly is inserted into thehole 18 of plug 10 and positioned firmly so that anode 22 is set flushin recess 25. The other-recess 30 is now filled with cement or resin 32and contact 34 is now spot-welded to other end of stem 20. The fin- 3ishing touches are provided by placing a heated ring adjacent the edgeof anode 22 so that the plastic of the plug 14 softens and is upset toform a heat seal bead 36 around the periphery of the anode 22.

Platinum and palladium-platinum alloys, because of their unique physicaland electrochemical properties, have been proposed as anode materialsand have been suc cessfully applied in several instances. In spite oftheir desirable properties of electrochemical inertness, electricalconductivity and mechanical workability, the high cost generallyassociated with these materials has nevertheless restricted theirapplication to specialized fields; however, in more recent years, theavailability of platinum-clad materials at much reduced costs has led toincreased appearance of these anodes in cathodic protection systems. Thecost of these platinum-clad materials was proportional to the thicknessof the cladding specified and to the complexity of completely claddingdifiicult geometric shapes. The serious drawback to platinum-cladmaterials prior to relatively recent developments was that a pore-freecladding had to be applied over common basis materials such as silver orcopper in order to prevent their electrochemical deterioration. Sealingthe edges of clad silver or cop per was also troublesome.

These objections to platinum-clad anodes were finally overcome by thecommercial introduction of rectifier metals such as tantalum andtitanium, which led to the development of platinum-coated anodes ofthese materials. Tantalum and titanium exhibit an interesting propertywhen anodized in sea-water and most aqueous media. An insulating film isformed on the surface which gradually increases in electrical resistanceuntil current can no longer pass into the electrolyte. This insulatingfilm is stable up to certain puncture voltages, above which film ruptureoccurs and electrochemical deterioration of the exposed metal ensues.The film formed on titanium in sea-water is stable up to 12 voltsapplied across the film. Tantalum on the other hand exhibits stabilityup to 130 volts in certain acid media. However, the protective film ontan talum forms in steps whereby a new film forms at a charactcristicvoltage. When a rupture occurs at a particular voltage, instead ofelectrochemical deterioration taking place a new film usually of adifferent color forms at the next corresponding voltage level and so onup to 130 volts. These protective films can conduct electronic currentwhen in contact with another metal despite their nonconducting nature inan electrolyte. These films are generally considered to be oxides.

The combination of platinum cladding or plating on titanium or tantalumhas resulted in a low-cost anode capable of passing high currentdensities without deterioration of the basic metal. These platinumcoatings no longer depend on continuity nor do they have to be pore-freeto perform inertly. The low electrode-electrolyte interface resistancebetween platinum and sea-water or other conductive aqueous media permitsthe stable oxide layer to form on the supporting titanium or tantalumbecause the voltage across the oxide is kept within safe limits.

Referring to FIGS. 2 and 3, a cross-section view of a centrifugal pumpis shown having a shaft 40, impeller blades 42, and a pump housing 44.

Housing 44 has a peripheral outlet 58 and a central inlet 60 as is shownon FIG. 3 to allow a corrosive fluid such as seawater to be pumped. Pipeplug anodes 46 are arranged around the periphery of the outside wall ofthe pump housing 44 in threaded bossings 43. Consequently, thesurface-coat of the anode will be substantially flush with the end ofthe plug at the inner side of the Wall, and the nut and contact sectionsof the plug will be on the outer side of the wall.

A battery or other DC. power source 5% has its negative terminal 52connected by a brush 54 to the shaft 40 while the positive terminal 56is connected to the anodes 46. A negative connection is also made to thecasing through a variable resistance 53. Suitable shunts 55,

0.1 ohm in this case, are connected in the positive line to the anodeand negative return lines to pump impeller and easing. By means of asuitable portable voltmeter (not shown), calibrated in amperes, thecurrent division to the impeller and casing can be measured.

With the cathodic protection system connected as shown in FIGS. 2 and 3,a current of about 50 milliamperes per square foot of impeller and shaftsurface are required for a fluid flow through the pump of 15 feet persecond. As an example for a pump of 3200 g.p.m. flow, a total current of2 amperes at about 8 volts is required from D.C. power source 50.

This large current maintains the hydrogen polarization film and formsmetallic salt deposits on the impeller blades, shaft, and pump housingto eliminate the how of corrosive currents. In order to preventconcentration of the protective current at the housing areas near thepipe plug anodes, dielectric shields 62 are applied to an area aroundeach anode for several anode diameters. These shields may be made ofpolychloroprene rubber, vinyl, or epoxy-coal tar resins.

The current distribution to the impeller and casing is also regulated tosome extent by varying resistor 53. The current ratio between casing andimpeller is adjusted generally in the order of 1:3.

The electric current also evolves free oxygen and chlorine at the pipeplug anode which are very corrosive to many compounds. After extensivetesting and experimentation at Portsmouth and Boston Naval Shipyards, ithas been found that only a few materials have been found to have therequired corrosion resistance and mechanical strength.

It is preferred to mold the pipe plug anode out of anacrylo-nitrile-butadiene styrene copolymer or glass-fiber reinforcedpolyester resin copolymer.

The pipe plug anode thus provides an insoluble cathodic protective anodewhich allows a large current output in a compact space while offeringnegligible resistance to rotating parts or fluid flow.

in addition the plastic pipe plug anode uses standard pipe fittings andprovides an excellent pressure or vacuum proof seal by virtue of itsability to deform easily and evenly around its circumference.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and that it isintended to cover all changes and modifications of the example of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention.

What is claimed is:

1. An article of manufacture adapted to be screwed in a wall as part ofa cathodic protection system, comprising a plastic plug, said plugcomprising a three-section insulating body consisting of a round firstthreaded section providing an inner end-portion for said plug andadapted to be screwed in a wall, a nut section contiguous to saidthreaded section and adapted to be operated by standard tools fortightening the plug in the wall, and a round second threaded contactsection contiguous to said nut section providing an outer end-portionfor said plug and adapted to receive a standard screw connector, saidfirst threaded section having an inner end face, said plug having acentral hole coaxial with said threaded sections, a metallic stemwater-tightly non-detachably fixed in said hole having a small diameteras compared with said first threaded section whereby the plug may deformaround its circumference as the plug is tightened in the well, said stembeing slightly shorter than said insulating body, an anode disc having adiameter larger than said stem and hole but smaller than said firstthreaded section. said anode disc being electrically and non-detachablymechanically secured to the end of said stem adjacent said inner endface, said end face being provided with a recess of. a size fittinglyreceiving said anode disc with a surface of the anode disc exposed andsubstantially flush with said end face, said anode consistingessentially of a metal chosen from the group consisting of titanium andtantalum and having a platinum coating on the last said surface, and acontact member electrically and non-detachably mechanically secured tothe outer end of said stem and in contact with said second threadedsection, said contact member having a diameter larger than said stem andhole but smaller than said second threaded section.

2. The plug anode as defined in claim 1 wherein the body of the plasticplug is made of a plastic consisting of one of the group consisting ofacrylonitrile-butadiene, styrene co polyrner and fiberglass reinforcedpolyester resin.

3. The plug anode as set forth in claim 1 further comprising a head ofthe material of the body of the plug overlapping the edge of said anodedisc thereby sealing the anode disc within the structure of the plug.

References Cited in the file of this patent UNITED STATES PATENTS393,072 Marquand u Nov. 20, 1888 921,641 Cumberland May 11, 19091,477,099 Baum Dec. 11, 1923 1,514,903 Gush Nov. 11, 1924 2,276,714Brown Mar. 17, 1942. 2,433,156 'Pezzillo Dec. 23, 1947 2,719,797Rosenblatt et al Oct. 4, 1955 2,878,173 Obermann Mar. 17, 1959 2,910,419Preiser et a1 Oct. 27, 1959 2,949,417 Preiser et a1 Aug, 16, 1960

1. AN ARTICLE OF MANUFACTURE ADAPTED TO BE SCREWED IN A WALL AS PART OFA CATHODIC PROTECTION SYSTEM, COMPRISING A PLASTIC PLUG, SAID PLUGCOMPRISING A THREE-SECTION IN SULATING BODY CONSISTING OF A ROUND FIRSTTHREADED SECTION PROVIDING AN INNER END-PORTION FOR SAID PLUG ANDADAPTED TO BE SCREWED IN A WALL, A NUT SECTION CONTIGUOUS TO SAIDTHREADED SECTION AND ADAPTED TO BE OPERATED BY STANDARD TOOLS FORTIGHTENING THE PLUG IN THE WALL, AND A ROUND SECONE THREADED CONTACTSECTION CONTIGUOUS TO SAID NUT SECTION PROVIDING AN OUTER END-PORTIONFOR SAID PLUG AND ADAPTED TO RECEIVE A STANDARD SCREW CONNECTOR, SAIDFIRST ITS CIRCUMFERENCE AS THE PLUG IS TIGHTENED IN THE WALL, SAID STEMBEING SLIGHTLY SHORTER THAN SAID INSULATING BODY, AN METALLIC STEMWATER-TIGHTLY NON-DETACHABLY FIXED IN SAID HOLE HAVING A SMALL DIAMETERAS COMPARED WITH SAID FIRST THREADED SECTION WHEREBY THE PLUG MAY DEFORMAROUND ITS CIRCUMFERENCE AS THE PLUG MAY DEFORM AROUND STEM BEINGSLIGHTLY SHORTER THAN SAID INSULATING BODY, AN ANODE DISC HAVING ADIAMETER LARGER THAN SAID STEM AND